Controlled-viscosity cmp casting method

ABSTRACT

The invention provides a method of manufacturing a polishing pad suitable for planarizing at least one of semiconductor, optical and magnetic substrates. The method obtains a liquid polyurethane material formed from an isocyanate-terminated molecule and a curative agent. The liquid polyurethane material contains 4.2 to 7.5 weight percent fluid-filled polymeric microspheres in the isocyanate-terminated molecule. The fluid-filled polymeric microspheres are a blend of preexpanded and unexpanded fluid-filled polymeric microspheres. The liquid polyurethane material contains a blend of preexpanded and unexpanded fluid-filled polymeric microspheres having a relative viscosity 
     
       
         
           
             μ 
             
               μ 
               0 
             
           
         
       
     
     of 1.1 to 7. Then the liquid polyurethane material solidifies into a polyurethane matrix that contains preexpanded and expanded fluid-filled polymeric microsphere for forming the polishing pad.

BACKGROUND

This specification relates to manufacturing polishing pads useful forpolishing and planarizing semiconductor, optical and magneticsubstrates.

Polyurethane polishing pads are the primary pad-type for a variety ofdemanding precision polishing applications. These polyurethane polishingpads are effective for polishing silicon wafers, patterned wafers, flatpanel displays and magnetic storage disks. In particular, polyurethanepolishing pads provide the mechanical integrity and chemical resistancefor most polishing operations used to fabricate integrated circuits. Forexample, polyurethane polishing pads have high strength for resistingtearing; abrasion resistance for avoiding wear problems duringpolishing; and stability for resisting attack by strong acidic andstrong caustic polishing solutions.

The production of semiconductors typically involves several chemicalmechanical planarization (CMP) processes. In each CMP process, apolishing pad in combination with a polishing solution, such as anabrasive-containing polishing slurry or an abrasive-free reactiveliquid, removes excess material in a manner that planarizes or maintainsflatness for receipt of a subsequent layer. The stacking of these layerscombines in a manner that forms an integrated circuit. The fabricationof these semiconductor devices continues to become more complex due torequirements for devices with higher operating speeds, lower leakagecurrents and reduced power consumption. In terms of device architecture,this translates to finer feature geometries and increased metallizationlevels. In some applications, these increasingly stringent device designrequirements are driving the adoption of increased number of tungsteninterconnect plugs or vias in conjunction with new dielectric materialshaving lower dielectric constants. The diminished physical properties,frequently associated with low k and ultra-low k materials, incombination with the devices' increased complexity have led to greaterdemands on CMP consumables, such as polishing pads and polishingsolutions.

In order to maintain consistent wafer throughput, semiconductorfabricators have practiced in-situ conditioning with diamond disks foryears. In-situ conditioning cuts the polishing pads top surface duringpolishing. A one-hundred percent in-situ conditioning processdiamond-conditions during the entire polishing process. A fifty-percentin-situ conditioning process conditions over one-half the polishingprocess. This conditioning process is essential to roughen the polishingsurface to maintain removal rate by preventing glazing of the polishingpad. In addition, these pads must polish with consistent rates overhundreds of wafers.

Casting polyurethane into cakes and cutting the cakes into several thinpolishing pads has proven to be an effective method for manufacturingpolishing pads with consistent reproducible polishing properties.Reinhardt et al., in U.S. Pat. No. 5,578,362, disclose the use ofpolymeric microspheres to improve planarization while maintaining lowdefectivity. Unfortunately, commercial polyurethane pads produced withthis structure often have rates that are sensitive to the diamondconditioner and conditioning process. In particular, as the diamondswear on the conditioner, they cut shallower channels into the polishingpad and these shallower channels can result in lower polishing removalrates.

In interlayer dielectric (ILD) polishing with fumed silica slurry,removal rate (RR) of a polishing pad is very sensitive to diamondconditioning. Without in-situ conditioning, the RR deteriorates rapidlywithin a few wafers of polishing, see FIG. 1. Although one-hundredpercent in-situ conditioning is typically used in ILD polishing with afumed silica slurry, high RR sensitivity to conditioning can stillresult in performance variation as a result of wear of conditioning diskover pad life. Therefore, there is a need for a polishing pad withreduced sensitivity to conditioning without sacrificing its polishingefficiency. Furthermore, there is a need to develop an effective methodfor manufacturing these and other CMP polishing pads.

STATEMENT OF INVENTION

An aspect of the invention provides a method of manufacturing apolishing pad suitable for planarizing at least one of semiconductor,optical and magnetic substrates, the method comprising the following:obtaining a liquid polyurethane material formed from anisocyanate-terminated molecule and a curative agent, the liquidpolyurethane material having a T_(gel) temperature and containing 4.2 to7.5 weight percent fluid-filled polymeric microspheres in theisocyanate-terminated molecule, the fluid-filled polymeric microspheresare a blend of preexpanded and unexpanded fluid-filled polymericmicrospheres, the preexpanded and unexpanded fluid-filled polymericmicrospheres each having a T_(start) temperature where diameter of thepreexpanded and unexpanded fluid-filled polymeric microspheres increasesat temperatures equal to or above the T_(start) temperature, with theT_(start) temperature of the unexpanded fluid-filled polymericmicrospheres being less than the T_(gel) temperature of the liquidpolyurethane material; casting the liquid polyurethane materialcontaining the blend of preexpanded and unexpanded fluid-filledpolymeric microspheres, the liquid polyurethane material containing theblend of preexpanded and unexpanded fluid-filled polymeric microsphereshaving a relative viscositf

$\frac{\mu}{\mu_{0}}$

of 1.1 to 7, wherein

$\frac{\mu}{\mu_{0}} = {1 + {2.5\varphi} + {10.05\varphi^{2}} + {0.00273^{16.6\varphi}}}$

where μ is the viscosity of the filled system, μ₀ the viscosity of theunfilled material,

$\frac{\mu}{\mu_{0}}$

the relative viscosity, and Φ the volume fraction of the filler, heatingand curing the liquid polyurethane material and the blend of prexpandedand unexpanded fluid-filled polymeric microspheres to a temperature ofat least T_(start) of the unexpanded fluid-filled polymeric microspheresto increase the diameter of the unexpanded fluid-filled polymericmicrospheres and to form a blend of preexpanded and expandedfluid-filled polymeric microspheres in the liquid polyurethane materialand then solidify the liquid polyurethane material into a polyurethanematrix containing the preexpanded and expanded fluid-filled polymericmicrospheres; and forming the polishing pad from the polyurethane matrixcontaining the preexpanded and expanded fluid-filled polymericmicrospheres.

Another aspect of the invention provides a method of manufacturing apolishing pad suitable for planarizing at least one of semiconductor,optical and magnetic substrates, the method comprising the following:obtaining a liquid polyurethane material formed from anisocyanate-terminated molecule and a curative agent, the liquidpolyurethane material having a T_(gel) temperature and containing 4.2 to7.5 weight percent fluid-filled polymeric microspheres in theisocyanate-terminated molecule, the fluid-filled polymeric microspheresare a blend of preexpanded and unexpanded fluid-filled polymericmicrospheres filled with isobutane, isopentane or a mixture of isobutaneand isopentane, the preexpanded and unexpanded fluid-filled polymericmicrospheres each having a T_(start) temperature where diameter of thepreexpanded and unexpanded fluid-filled polymeric microspheres increasesat temperatures equal to or above the T_(start) temperature, with theT_(start) temperature of the unexpanded fluid-filled polymericmicrospheres being less than the T_(gel) temperature of the liquidpolyurethane material; casting the liquid polyurethane materialcontaining the blend of preexpanded and unexpanded fluid-filledpolymeric microspheres, the liquid polyurethane material containing theblend of preexpanded and unexpanded fluid-filled polymeric microsphereshaving a relative viscosity

$\frac{\mu}{\mu_{0}}$

of 1.1 to 7, wherein

$\frac{\mu}{\mu_{0}} = {1 + {2.5\varphi} + {10.05\varphi^{2}} + {0.00273^{16.6\varphi}}}$

where p is the viscosity of the filled system, go the viscosity of theunfilled material,

$\frac{\mu}{\mu_{0}}$

the relative viscosity, and Φ the volume fraction of the filler; heatingand curing the liquid polyurethane material and the blend of prexpandedand unexpanded fluid-filled polymeric microspheres to a temperature ofat least T_(start) of the unexpanded fluid-filled polymeric microspheresto increase the diameter of the unexpanded fluid-filled polymericmicrospheres and to form a blend of preexpanded and expandedfluid-filled polymeric microspheres in the liquid polyurethane materialand then solidify the liquid polyurethane material into a polyurethanematrix containing the preexpanded and expanded fluid-filled polymericmicrospheres; and forming the polishing pad from the polyurethane matrixcontaining the preexpanded and expanded fluid-filled polymericmicrospheres.

DESCRIPTION OF THE DRAWING

FIG. 1 is a plot of removal rate in Å/min versus wafer number afterstopping in-situ conditioning for Semi-Sperse™ 25E (SS25) fumed silicaslurry. (Semi-Sperse is a trademark of Cabot MicroelectronicsCorporation.)

FIG. 2 is a plot of average removal rate in Å/min and within-wafernon-uniformity (WIW-NU) (%) for ILD polishing.

FIG. 3 is an SEM of preexpanded and unexpanded fluid-filled microspheresat a concentration of 8 wt %.

FIG. 4 is an SEM of preexpanded and unexpanded fluid-filled microspheresat a concentration of 5.25 wt % formed with an MbOCA curative.

FIG. 4A is a size distribution plot of diameter measured in micrometersfor the polishing pad of FIG. 4.

FIG. 5 is an SEM of preexpanded and unexpanded fluid-filled microspheresat a concentration of 5.25 wt % formed with an MbOCA curative blendedwith a multifunctional polyol.

FIG. 5A is a size distribution plot of diameter measured in micrometersfor the polishing pad of FIG. 5.

FIG. 6 is a plot of relative viscosity versus volume fraction solidsaccording to a modified Einstein-Guth-Gold equation.

FIG. 7 is a plot of relative viscosity versus weight percent polymericmicrospheres for preexpanded, unexpanded, and blends of preexpanded andunexpanded polymeric microspheres.

DETAILED DESCRIPTION

The invention provides a polishing pad suitable for planarizing at leastone of semiconductor, optical and magnetic substrates. The polishing padhas a top polishing surface, comprising a reaction product of anisocyanate-terminated prepolymer and a curative system. The toppolishing layer further comprises polymeric microspheres at a levelbetween above 4 and less than 8 weight percent of the prepolymer. Thesepolishing pads have higher removal rate, better within wafer uniformity,and reduced sensitivity to conditioning process.

The polishing pad contains 4.2 to 7.5 weight percent fluid-filledmicrospheres in the prepolymer. Preferably, the polishing pad contains4.5 to 7.5 weight percent fluid-filled microspheres in the prepolymer.Most preferably, the polishing pad contains 5 to 7.5 weight percentfluid-filled microspheres in the prepolymer. This leads to a low densityor high porosity polishing pad with controlled pore size. For example,the final density may be 0.5 to 0.75 g/cm³. Preferably, the finaldensity is 0.5 to 0.65 g/cm³.

The fluid filling the microspheres can be a gas, liquid or a combinationof gas and liquid. If the fluid is a liquid, then the preferred fluid iswater, such as distilled water that only contains incidental impurities.For purposes of this application the term microsphere includes shellswith less than a perfect spherical shape; for example, these shells havewhat appears to be a semi-hemispherical shape when cut open and viewedwith an SEM. If the fluid is a gas, then air, nitrogen, argon, carbondioxide or combination thereof is preferred. For some microspheres, thegas may be an organic gas, such as isobutane. Preferably, the fluid isisobutane, isopentane or a combination of isobutane and isopentane.Isobutane trapped in the polymeric microsphere is gas at roomtemperature (25° C.) and above, depending upon internal pressure in thepolymeric shell. Isopentane trapped in the polymeric microsphere is acombination of liquid and gas at room temperature. At temperatures ofabout 30° C. and above, the isopentane becomes gas—depending uponinternal pressure in the polymeric shell. A polymeric shell holds thefluid; and typically the polymeric shell holds gas under pressure.Specific examples of the polymer shell includepolyacrylonitrile/methacrylonitrile shells and poly(vinylidenedichloride)/polyacrylonitrile shells. Furthermore, these shells mayincorporate inorganic particles, such as silicates, calcium-containingor magnesium-containing particles. These particles facilitate separationof the polymeric microspheres. These fluid-filled-microspheres typicallyhave an average final average diameter of 10 to 80 μm after expansionand preferably, 20 to 60 μm. Preexpanded polymeric microspherestypically grow 10 to 60 percent to a final average diameter of 20 to 150μm. Unexpanded polymeric microspheres, however, typically grow 1,000 to10,000 percent to a final diameter of 20 to 150 μm. The resulting blendof polymeric microspheres in the solidified polymeric matrix has a finalaverage diameter of 10 to 80 μm after expansion and preferably, 20 to 60μm.

The polishing pad optionally contains silica-containing or alkalineearth (Group IIA of the Periodic Table) metal oxide-containing regionsdistributed within each of the polymeric microspheres. Thesesilica-containing or alkaline earth metal oxide-containing regions maybe particles or have an elongated alkaline earth metal oxide-containingstructure. Typically, the alkaline earth metal oxide-containing regionsrepresent particles embedded or attached to the polymeric microspheres.The average particle size of the alkaline earth metal oxide-containingparticles is typically 0.01 to 3 μm. Preferably, the average particlesize of the alkaline earth metal oxide-containing particles is 0.01 to 2μm. These alkaline earth metal oxide-containing particles are spaced tocoat less than 50 percent of the outer surface of the polymericmicrospheres. Preferably, the alkaline earth metal oxide-containingregions cover 1 to 40 percent of the surface area of the polymericmicrospheres. Most preferably, the alkaline earth metal oxide-containingregions cover 2 to 30 percent of the surface area of the polymericmicrospheres. The silica-containing or alkaline earth metaloxide-containing microspheres have a density of 5 g/liter to 1,000g/liter. Typically, the alkaline earth metal oxide-containingmicrospheres have a density of 10 g/liter to 1,000 g/liter.

Typical polymeric polishing pad matrix materials include polycarbonate,polysulfone, polyamides, ethylene copolymers, polyethers, polyesters,polyether-polyester copolymers, acrylic polymers, polymethylmethacrylate, polyvinyl chloride, polyethylene copolymers,polybutadiene, polyethylene imine, polyurethanes, polyether sulfone,polyether imide, polyketones, epoxies, silicones, copolymers thereof andmixtures thereof. Preferably, the polymeric material is a polyurethane;and may be either a cross-linked a non-cross-linked polyurethane. Forpurposes of this specification, “polyurethanes” are products derivedfrom difunctional or polyfunctional isocyanates, e.g. polyetherureas,polyisocyanurates, polyurethanes, polyureas, polyurethaneureas,copolymers thereof and mixtures thereof.

Preferably, the polymeric material is a block or segmented copolymercapable of separating into phases rich in one or more blocks or segmentsof the copolymer. Most preferably, the polymeric material is apolyurethane. Cast polyurethane matrix materials are particularlysuitable for planarizing semiconductor, optical and magnetic substrates.An approach for controlling a pad's polishing properties is to alter itschemical composition. In addition, the choice of raw materials andmanufacturing process affects the polymer morphology and the finalproperties of the material used to make polishing pads.

Preferably, urethane production involves the preparation of anisocyanate-terminated urethane prepolymer from a polyfunctional aromaticisocyanate and a prepolymer polyol. For purposes of this specification,the term prepolymer polyol includes diols, polyols, polyol-diols,copolymers thereof and mixtures thereof. Preferably, the prepolymerpolyol is selected from the group comprising polytetramethylene etherglycol [PTMEG], polypropylene ether glycol [PPG], ester-based polyols,such as ethylene or butylene adipates, copolymers thereof and mixturesthereof. Example polyfunctional aromatic isocyanates include 2,4-toluenediisocyanate, 2,6-toluene diisocyanate, 4,4′-diphenylmethanediisocyanate, naphthalene-1,5-diisocyanate, tolidine diisocyanate,para-phenylene diisocyanate, xylylene diisocyanate and mixtures thereof.The polyfunctional aromatic isocyanate contains less than 20 weightpercent aliphatic isocyanates, such as 4,4′-dicyclohexylmethanediisocyanate, isophorone diisocyanate and cyclohexanediisocyanate.Preferably, the polyfunctional aromatic isocyanate contains less than 15weight percent aliphatic isocyanates and more preferably, less than 12weight percent aliphatic isocyanate.

Example prepolymer polyols include polyether polyols, such as,poly(oxytetramethylene)glycol, poly(oxypropylene)glycol and mixturesthereof, polycarbonate polyols, polyester polyols, polycaprolactonepolyols and mixtures thereof. Example polyols can be mixed with lowmolecular weight polyols, including ethylene glycol, 1,2-propyleneglycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol,2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol,1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, diethyleneglycol, dipropylene glycol, tripropylene glycol and mixtures thereof.

Preferably the prepolymer polyol is selected from the group comprisingpolytetramethylene ether glycol, polyester polyols, polypropylene etherglycols, polycaprolactone polyols, copolymers thereof and mixturesthereof. If the prepolymer polyol is PTMEG, copolymer thereof or amixture thereof, then the isocyanate-terminated reaction productpreferably has a weight percent unreacted NCO range of 8.0 to 20.0weight percent. For polyurethanes formed with PTMEG or PTMEG blendedwith PPG, the preferable weight percent NCO is a range of 8.75 to 12.0;and most preferably it is 8.75 to 10.0. Particular examples of PTMEGfamily polyols are as follows: Terathane® 2900, 2000, 1800, 1400, 1000,650 and 250 from Invista; Polymeg® 2900, 2000, 1000, 650 from Lyondell;PolyTHF® 650, 1000, 2000 from BASF, and lower molecular weight speciessuch as 1,2-butanediol, 1,3-butanediol, and 1,4-butanediol. If theprepolymer polyol is a PPG, copolymer thereof or a mixture thereof, thenthe isocyanate-terminated reaction product most preferably has a weightpercent unreacted NCO range of 7.9 to 15.0 wt. %. Particular examples ofPPG polyols are as follows: Arcol® PPG-425, 725, 1000, 1025, 2000, 2025,3025 and 4000 from Bayer; Voranol® 1010L, 2000L, and P400 from Dow;Desmophen® 1110BD, Acclaim® Polyol 12200, 8200, 6300, 4200, 2200 bothproduct lines from Bayer. If the prepolymer polyol is an ester,copolymer thereof or a mixture thereof, then the isocyanate-terminatedreaction product most preferably has a weight percent unreacted NCOrange of 6.5 to 13.0. Particular examples of ester polyols are asfollows: Millester 1, 11, 2, 23, 132, 231, 272, 4, 5, 510, 51, 7, 8, 9,10, 16, 253, from Polyurethane Specialties Company, Inc.; Desmophen®1700, 1800, 2000, 2001KS, 2001K2, 2500, 2501, 2505, 2601, PE65B fromBayer; Rucoflex S-1021-70, S-1043-46, S-1043-55 from Bayer.

Typically, the prepolymer reaction product is reacted or cured with acurative polyol, polyamine, alcohol amine or mixture thereof. Forpurposes of this specification, polyamines include diamines and othermultifunctional amines. Example curative polyamines include aromaticdiamines or polyamines, such as, 4,4′-methylene-bis-o-chloroaniline[MbOCA], 4,4′-methylene-bis-(3-chloro-2,6-diethylaniline) [MCDEA];dimethylthiotoluenediamine; trimethyleneglycol di-p-aminobenzoate;polytetramethyleneoxide di-p-aminobenzoate; polytetramethyleneoxidemono-p-aminobenzoate, polypropyleneoxide di-p-aminobenzoate;polypropyleneoxide mono-p-aminobenzoate;1,2-bis(2-aminophenylthio)ethane; 4,4′-methylene-bis-aniline;diethyltoluenediamine; 5-tert-butyl-2,4- and3-tert-butyl-2,6-toluenediamine; 5-tert-amyl-2,4- and3-tert-amyl-2,6-toluenediamine and chlorotoluenediamine. Optionally, itis possible to manufacture urethane polymers for polishing pads with asingle mixing step that avoids the use of prepolymers.

The components of the polymer used to make the polishing pad arepreferably chosen so that the resulting pad morphology is stable andeasily reproducible. For example, when mixing4,4′-methylene-bis-o-chloroaniline [MbOCA] with diisocyanate to formpolyurethane polymers, it is often advantageous to control levels ofmonoamine, diamine and triamine. Controlling the proportion of mono-,di- and triamines contributes to maintaining the chemical ratio andresulting polymer molecular weight within a consistent range. Inaddition, it is often important to control additives such asanti-oxidizing agents, and impurities such as water for consistentmanufacturing. For example, since water reacts with isocyanate to formgaseous carbon dioxide, controlling the water concentration can affectthe concentration of carbon dioxide bubbles that form pores in thepolymeric matrix. Isocyanate reaction with adventitious water alsoreduces the available isocyanate for reacting with chain extender, sochanges the stoichiometry along with level of crosslinking (if there isan excess of isocyanate groups) and resulting polymer molecular weight.

The polyurethane polymeric material is preferably formed from aprepolymer reaction product of toluene diisocyanate andpolytetramethylene ether glycol with an aromatic diamine. Mostpreferably the aromatic diamine is 4,4′-methylene-bis-o-chloroaniline or4,4′-methylene-bis-(3-chloro-2,6-diethylaniline). Preferably, theprepolymer reaction product has a 6.5 to 15.0 weight percent unreactedNCO. Examples of suitable prepolymers within this unreacted NCO rangeinclude: Imuthane® prepolymers PET-70D, PHP-70D, PET-75D, PHP-75D,PPT-75D, PHP-80D manufactured by COIM USA, Inc. and Adiprene®prepolymers, LFG740D, LF700D, LF750D. LF751D, LF753D, L325 manufacturedby Chemtura. In addition, blends of other prepolymers besides thoselisted above could be used to reach to appropriate percent unreacted NCOlevels as a result of blending. Many of the above-listed prepolymers,such as, LFG740D, LF700D, LF750D, LF751D, and LF753D are low-freeisocyanate prepolymers that have less than 0.1 weight percent free TDImonomer and have a more consistent prepolymer molecular weightdistribution than conventional prepolymers, and so facilitate formingpolishing pads with excellent polishing characteristics. This improvedprepolymer molecular weight consistency and low free isocyanate monomergive a more regular polymer structure, and contribute to improvedpolishing pad consistency. For most prepolymers, the low free isocyanatemonomer is preferably below 0.5 weight percent. Furthermore,“conventional” prepolymers that typically have higher levels of reaction(i.e. more than one polyol capped by a diisocyanate on each end) andhigher levels of free toluene diisocyanate prepolymer should producesimilar results. In addition, low molecular weight polyol additives,such as, diethylene glycol, butanediol and tripropylene glycolfacilitate control of the prepolymer reaction product's weight percentunreacted NCO.

Similarly, the polyurethane polymeric material may be formed from aprepolymer reaction product of 4,4′-diphenylmethane diisocyanate (MDI)and polytetramethylene glycol with a diol. Most preferably, the diol is1,4-butanediol (BDO). Preferably, the prepolymer reaction product has 6to 13 wt % unreacted NCO. Examples of suitable polymers with thisunreacted NCO range include the following: Imuthane 27-85A, 27-90A,27-95A, 27-52D, 27-58D from COIM USA and Andur®@E-75AP, IE80AP, IE90AP,IE98AP, IE110AP prepolymers from Anderson Development Company.

In addition to controlling weight percent unreacted NCO, the curativeand prepolymer reaction product typically has an OH or NH2 to unreactedNCO stoichiometric ratio of 85 to 115 percent, preferably 90 to 100percent. This stoichiometry could be achieved either directly, byproviding the stoichiometric levels of the raw materials, or indirectlyby reacting some of the NCO with water either purposely or by exposureto adventitious moisture.

The polishing pad has less sensitivity to conditioner wear than mostpolishing pads. This is particularly useful for combating the adverseimpact of diamond wear. Pads of the invention can have a conditionersensitivity (CS) of 0 to 2.6. Preferably the CS is 0 to 2. For purposeof this application, CS is defined as follows:

$\begin{matrix}{{CS} = {\frac{{{RR}_{75\% \mspace{14mu} {In}\text{-}{situ}\mspace{14mu} {{Conditionin}g}} - {RR}_{50\% \mspace{14mu} {In}\text{-}{situ}\mspace{14mu} {Conditioning}}}}{{RR}_{50\% \mspace{14mu} {In}\text{-}{situ}\mspace{14mu} {Conditioning}}} \times 100\%}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

where CS is defined as blanket TEOS removal rate at 75% in-situconditioning (RR_(75% In-situ Conditioning)) and blanket TEOS removalrate at 50% in-situ conditioning (RR_(50% In-situ Conditioning)) dividedby the blanket TEOS removal rate at 50% partial in-situ conditioningusing a fumed silica slurry having a 0.1 μm average particle size at a12.5 wt % concentration with a pH of 10.5 (all after being diluted withdistilled water at a 1:1 ratio) with a diamond conditioner with a 150 μmaverage particle size, a 400 μm pitch and a 100 μm protrusion at aconditioner downforce of 9 lbs (or 4.08 Kg). The CS removal rate valuesrepresent the removal rate achieved after reaching steady statepolishing or typically at least after about ten wafers.

There are significant challenges in making CMP polishing pads withpreexpanded polymeric microspheres at level above 4 weight percent inprepolymer, due to exponential increase of material viscosity withincreasing loading of preexpanded polymeric microspheres. Theintroduction of unexpanded polymeric microspheres that can expand fromthe reaction exotherm of the prepolymer and the curative system not onlyreduced material viscosity for easy processing, but also resulted inbetter product consistency and higher production yield.

During production, a liquid polyurethane material has a T_(gel)temperature and contains fluid-filled polymeric microspheres. Thefluid-filled polymeric microspheres are a blend of preexpanded andunexpanded fluid-filled polymeric microspheres. The preexpanded andunexpanded fluid-filled polymeric microspheres each have a T_(start)temperature where diameter of the preexpanded and unexpandedfluid-filled polymeric microspheres increases at temperatures equal toor above the T_(start) temperature. In addition, they have a T_(max)temperature where gas escapes through the fluid-filled polymericmicrospheres to decrease diameter of polymeric microspheres. Becausethis can form large gas bubbles in the polymer matrix and large bubblescan result in polishing defects, casting at or above the T_(max)temperature is not a desireable situation. In order to grow theunexpanded polymeric microspheres, it is important that the T_(start)temperature of the unexpanded fluid-filled polymeric microspheres beless than the T_(gel) temperature of the liquid polyurethane material.Advantageously, the T_(start) temperature of the unexpanded fluid-filledpolymeric microspheres is at least 5° C. less than the T_(gel)temperature of the liquid polyurethane material. Advantageously, theT_(start) temperature of the unexpanded fluid-filled polymericmicrospheres is at least 10° C. less than the T_(gel) temperature of theliquid polyurethane material. As the preexpanded already have aneffective average diameter, there is no need for further growth and itis optional for the T_(start) temperature of the preexpandedfluid-filled polymeric microspheres be less than the T_(gel) temperatureof the liquid polyurethane material.

Then casting the liquid polyurethane material containing the blend ofpreexpanded and unexpanded fluid-filled polymeric microspheres reactsthe isocyanate-terminated molecule and the curative agent. Exothermicheat from the reaction, heats the blend of preexpanded and unexpandedfluid-filled polymeric microspheres in the liquid polyurethane materialto a temperature of at least T_(start) of the unexpanded fluid-filledpolymeric microspheres to increase the diameter of the unexpandedfluid-filled polymeric microspheres. Preferably this exothermic heat isthe primary heat source to drive expansion to the polymericmicrospheres. The heating is to a temperature less than the T_(max)temperature where gas escapes through the preexpanded and unexpandedfluid-filled polymeric microspheres. This heating forms a blend ofpreexpanded and expanded fluid-filled polymeric microspheres in theliquid polyurethane material. Optionally, mixing the blend ofpreexpanded and unexpanded polymeric microspheres in the liquidpolyurethane material before casting improves uniformity of thepolymeric microsphere distribution.

Curing the blend of preexpanded and expanded fluid-filled polymericmicrospheres in the liquid polyurethane material solidifies the liquidpolyurethane material into a polyurethane matrix containing thepreexpanded and expanded fluid-filled polymeric microspheres. Thenfinishing the cured polyurethane matrix containing the preexpanded andexpanded fluid-filled polymeric microspheres into a polishing pad byskiving, facing, grooving, perforating and adding a subpad creates afinished product. For example, when casting into a mold, it is possibleto skive the polishing pad into multiple polyurethane sheets, then formthe polishing pads from the polyurethane sheets. The final diameter ofthe preexpanded and expanded fluid-filled polymeric microspheres in thepolishing pad is less than that achieved from the T_(max) temperature inair and a majority of fluid contained in the preexpanded and unexpandedfluid-filled polymeric microspheres remains in the preexpanded andexpanded fluid-filled polymeric microspheres.

In addition, it is important that the liquid polyurethane material haslow viscosity to facilitate casting into consistent productconfigurations. Forming a blend of preexpanded and unexpanded polymericmicrospheres lowers viscosity to facilitate casting. This is ofparticular importance when casting around objects such as transparentblocks used to form transparent windows in the polishing pads. Apreexpanded only mixture can lack the viscosity required for pouringinto simple shapes. An unexpanded only mixture can create significantstress in a cake from large expansion of unexpanded microspheres. Thesestresses can result in a cracked or fractured polymeric matrix.Furthermore, it is advantageous that the majority of the heat requiredto expand the unexpanded polymeric microspheres arises from anexothermic reaction used to create the polymeric matrix. A blend ofpreexpanded and unexpanded polymeric microspheres having a relativeviscosity of 1.1 to 7, however, can have sufficient viscosity forcasting in combination with sufficient exothermic heat to createadequate porosity. Preferably, a relative viscosity of 3 to 7 provides abalanced combination of castability and pore size. Furthermore,increasing the proportion of unexpanded to preexpanded polymericmicrospheres decreases viscosity to improve the castability, butincreases the residual stress in the cake that can cause cake pop andother defects. Similarly, increasing the proportion of preexpanded tounexpanded polymeric microspheres can increase the viscosity to rendercasting more difficult.

EXAMPLES Example 1

Table 1 lists composition of the polishing layer of two comparativeexamples #C1 and #C2 and two examples from the present invention #1 and#2. The isocyanate-terminated prepolymer used was Adiprene® L325,commercially available from Chemtura Corporation, with typical unreactedisocyanate (NCO) of 9.1% by weight. The curative system was either4,4′-methylene-bis(2-chloroaniline) (MbOCA) or a combination of MbOCAand Voralux® HF 505, a high molecular weight (MW) multi-functionalpolyol curative with six hydroxyl functionalities and a MW about 11,000.The reaction stoichiometry, calculated by mol ratio of total activehydrogen (as amine and hydroxyl functional groups in the curativesystem) to isocyanate functional groups in the prepolymer, was 0.87 forall examples. Fluid-filled polymeric microspheres, both preexpanded (DE)and dry unexpanded (DU), were mixed with the prepolymer forming apreblend. Expancel® 551DE40d42, Expancel® 461DE20d70, both DE grades,and Expancel® 031DU40, a DU grade, are commercially available fromAkzoNobel. The amount of total polymeric microspheres varied from 2.2 to5.25 weight percent in the preblend (the mixture of the prepolymer andthe polymeric microspheres).

TABLE 1 Microsphere Multi- Microsphere Diameter MbOCA FunctionalDiameter Microsphere Unexpanded Microsphere Microsphere CurativeCurative Preexpanded Preexpanded (μm post- Unexpanded Total Example (wt%) (wt %) (μm) (wt %) expansion) (wt %) (wt %) C1 100 40* 2.2 2.2 C2 7525 20** 3.75 3.75 1 100 20** 3.75 40*** 1.5 5.25 2 75 25 20** 3.75 40***1.5 5.25 Adiprene ® is a urethane prepolymer products of ChemturaCorporation. Adiprene L325 is a urethane prepolymer of H₁₂MDI/TDI withpolytetramethylene ether glycol (PTMEG) having an unreacted NCO of 8.95to 9.25 wt %. *551DE40d42, **461DE20d70, and ***031DE40 551DE40d42,461DE20d70, and 031DE40 are fluid-filled polymeric microspheres made byAkzoNobel with tradename Expancel ®.

The polishing layer for all pad examples was finished with circular(1010) and radial (R32) overlaid grooves (1010+R32). A 1.02 mm (40 mil)thick Suba™ IV subpad was stacked to the polishing layer. The circular1010 grooves had a width of 0.51 mm (20 mils), depth of 0.76 mm (30mils) and a pitch of 3.05 mm (120 mils). The R-32 radial grooves were 32evenly spaced radial grooves with a width of 0.76 mm (30 mils) and adepth of 0.81 mm (32 mils).

The slurry used was a fumed silica based LD3225 slurry, commerciallyavailable from Nitta Haas Incorporated, having an average particle sizeabout 0.1 μm, diluted with de-ionized water at 1:1 ratio to 12.5 wt %abrasive at the point of use (POU) for polishing. The polishing wascarried out on a 300 mm CMP polishing system Reflexion® by AppliedMaterials. Polishing conditions are summarized below.

Polishing Conditions:

-   -   Slurry: ILD3225 (1:1 dilution with DI water to 12.5% abrasive        content; pH 10.5)    -   POU filter: Pall 1.5 μm    -   Slurry flow rate: 250 ml/min    -   Conditioner: PDA33A-3 by Kinik Company; 150 μm diamond size, 400        μm diamond pitch, 100±15 μm diamond protrusion.    -   Pad break-in: 90/108 rpm (platen/conditioning disk), 12 lbs (5.4        Kg) for 20 minutes followed by 9 lbs (4.1 Kg) downforce for 10        minutes; high pressure rise (HPR)    -   During polishing: full in-situ conditioning at 9 lbs (4.1 Kg)        conditioning downforce    -   Polishing: 93/87 rpm (platen/wafer), at 4.5 psi (31 KPa)        downforce for 60 seconds

Oxide polishing was performed on TEOS oxide wafers formed by chemicalvapor deposition (TEOS represents the decomposition product oftetraethyl orthosilicate). Removal rates and within-wafer non-uniformity(WIW-NU) are shown in FIG. 2 and also summarized in Table 2.

TABLE 2 Polishing Total Polymeric TEOS Within Wafer layer ofMicrospheres RR Non-Uniformity Normalized Ex. # wt % (Å/min) % RR C1 2.24546 3.5 100% C2 3.75 4685 2.8 103% 1 5.25 5002 2.6 110% 2 5.25 5066 2.5111%

FIG. 2 and Table 2 illustrate improved removal rate and WIW-NU for thepolishing pad of the invention.

Polishing pads from the current invention (Ex. #1 and #2), whichcontained more than 4 wt % of total polymeric microspheres in thepreblend, demonstrated higher TEOS removal rate, better within waferuniformity, than the comparative examples (Ex. #C1 and C2) which hadless than 4 wt % of total polymeric microspheres in the preblend.Surprisingly, polishing pads from the current invention had lesssensitivity to conditioning process in combination with high polishingefficiency. Conditioning sensibility (CS) is defined as RR difference at75% and 50% partial in-situ conditioning divided by the RR at 50%partial in-situ conditioning.

$\begin{matrix}{{CS} = {\frac{{{RR}_{75\% \mspace{14mu} {In}\text{-}{situ}\mspace{14mu} {{Conditionin}g}} - {RR}_{50\% \mspace{14mu} {In}\text{-}{situ}\mspace{14mu} {Conditioning}}}}{{RR}_{50\% \mspace{14mu} {In}\text{-}{situ}\mspace{14mu} {Conditioning}}} \times 100\%}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

As shown in Table 3, polishing pads from the current invention had CSless than 1% while comparative example #C1 had more than 3% CS. Thereduced CS is critical for stable polishing performance as conditioningdisks wear out over pad life.

TABLE 3 Total Polymeric TEOS RR (Å/min) Conditioning PolishingMicrospheres 75% partial 50% partial Sensibility layer of wt % in-situin-situ (CS) Ex. # C1 2.2 3890 3754 3.6% Ex. # 1 5.25 4864 4821 0.9% Ex.# 2 5.25 4961 4970 0.2%

Too much fluid-filled polymeric microspheres in the preblend couldresult in blown-out holes in the polishing layer, leading to non-uniformproduct and possibly inconsistent polishing performance. FIG. 3 showsblow-out holes present at 8 wt % fluid-filled polymeric microspheres.The sample in FIG. 3 had the same chemical composition (prepolymer andcurative) as comparative Ex. #C1 and Ex. #1 as shown in Table 1, buthigher loading of fluid-filled polymeric microspheres at 8 wt % ofExpancel 031DU40.

By comparison, both examples Ex. #1 and #2 from the current inventionshowed uniform pore structure in the polishing layer with normal poresize distribution, as shown in FIGS. 4 and 5, respectively.

Example 2

There have been significant challenges in casting high porosity (low SG)polymeric microsphere-filled polyurethane polishing pads in cake molds.The challenge became acerbated when an integral window was attempted.This was mainly due to poor flowability of a very viscous preblend andthe liquid polyurethane precursor.

The viscosity of a filled system increases dramatically with theincrease of the volume fraction of a filler, see FIG. 6 (Journal ofColloid Science, vol. 20, 267-277, 1965). David G. Thomas plottedrelative viscosity of a filled system with filler volume fraction Q andcame up with the following equation to predict viscosity of a filledsystem. FIG. 6 plots a modified Einstein-Guth-Gold equation thatdescribes viscosity of a suspension filled with spherical particles.

$\begin{matrix}{\frac{\mu}{\mu_{0}} = {1 + {2.5\varphi} + {10.05\varphi^{2}} + {0.00273^{16.6\varphi}}}} & \left( {{Equation}\mspace{14mu} 2} \right)\end{matrix}$

where μ is the viscosity of the filled system, μ₀ the viscosity of theunfilled material, μ/μ₀ the relative viscosity, and Φ the volumefraction of the filler.

Typical prepolymer specific gravity (SG) is about 1.05 g/cm³. With givenSG of fluid-filled polymeric microspheres, we can easily predictviscosity increase of a preblend at different loading levels offluid-filled polymeric microspheres by using Equation (3). The preblendviscosity will increase significantly with increasing loading ofpreexpanded polymeric microspheres. The results in Table 4 are forpreexpanded polymeric microspheres. Expancel 551DE40d42, Expancel551DE20d60, and Expancel 461DE20d70 all achieve numbers in excess of40μ/μ₀, at above 8 wt % of fluid-filled polymeric microspheres.

TABLE 4 wt % polymeric Relative viscosity of a filled system withmicrospheres 551DE40d42 551DE20d60 461DE20d70 0 1.0 1.0 1.0 1 2.0 1.61.5 2 3.7 2.6 2.3 3 7.8 4.0 3.3 4 18 6.8 5.1 5 40 12 8.2 6 80 23 14 7146 40 23 8 244 67 39

At typical prepolymer processing temperature of 50 to 70° C., mostcommercial prepolymers without any filler have viscosity in the range of1,000 to 5,000 cps, as shown in Table 5. There are numerous challengesin handling a preblend with viscosity significantly higher than 10,000cps in casting process, including defects like flow patterns. Increasingpreblend temperature to reduce viscosity is not feasible as the gel timecan become too short to pour a cake. As a result, the maximum fillerloading in a preblend is normally no more than 4 wt % for Expancel461DE20d70 polymeric microspheres or 2.5 wt % for Expancel 551DE40d42polymeric microspheres. At such filler loading levels, the relativeviscosity of the preblend to the unfilled prepolymer is about 5. Inother words, the viscosity of the preblend is about 5 times that of theunfilled prepolymer. Because of this limitation, the maximum volumeporosity is typically less than 40% for a polishing pad with porositygenerated by incorporating conventional preexpanded polymericmicrospheres. This translates into significant challenges in making CMPpolishing pads with SG lower than 0.70 using preexpanded polymericmicrospheres.

TABLE 5 Typical viscosity of commercial prepolymers without any fillerat various temperatures % NCO Typical viscosity Prepolymer rangeTemperature (C .) (cps) Adiprene L325 8.95-9.25 30 20,000 50 5000 701000 Adiprene 750D 8.75-9.05 30 10,500 60 1250 Adiprene 600D 7.1-7.4 306000 60 900 Adiprene LFG963A 5.55-5.85 30 15,000 50 3200 70 1000

To overcome viscosity limitations of a prepolymer containing greaterthan 4 to less than 8 wt % of polymeric microspheres, the presentinvention provides a method of making extra high porosity polishing padwith specific gravity values lower than 0.70 g/cm³ without significantlyincreasing the preblend viscosity.

Unexpanded polymeric microspheres occupy much less volume due to theirhigh initial specific gravity values (close to that of a prepolymer). Asa result, they fail to contribute much to the increase of preblendviscosity. These unexpanded polymeric microspheres can expand fromheating including reaction exotherm of a polyurethane prepolymerreacting with a curative system. As a result, extra high porosity withpad specific gravity values lower than 0.70 g/cm³ can be madeconsistently without the limitation of high preblend viscosity.

Ex #1 and #2 had very uniform pore structure, as shown in FIGS. 4, 4A, 5and 5A. Average pore size and standard deviation of Ex. #1, #2, andcomparative Ex. #C1 are summarized in Table 6.

TABLE 6 Polishing layer Average Pore Size Standard deviation of (μm)(μm) Ex. #C1 41 13 Ex. #1 25 10 Ex. #2 24 10

FIG. 7 shows relative viscosity comparison of a preblend containingdifferent types of fluid-filled polymeric microspheres. There are twoviable approaches to keep preblend viscosity in a reasonable range withabove 4 to less than 8 wt % loading of fluid-filled polymericmicrospheres. The first approach is to use only unexpanded polymericmicrospheres, such as Expancel 031DU40 polymeric microspheres. Theviscosity increase will be less than 50% at up to 8 wt % loading level.One alternative is to use a combination of preexpanded and unexpandedpolymeric microspheres. The amount of preexpanded polymericmicrospheres, such as Expancel 461DE20d70 polymeric microspheres, can bekept under 4 wt % to maintain reasonable preblend viscosity. Withspecific gravity values close to 1.0 g/cm³, unexpanded polymericmicrospheres, such as Expancel 031DU40 polymeric microspheres, do notcontribute much to preblend viscosity. At a total of 8 wt % loading offluid-filled polymeric microspheres, over one order of magnitudereduction in preblend viscosity can be achieved by introducingunexpanded polymeric microspheres such as Expancel 031DU40.

Example 3

Fluid-filled polymeric microspheres, either preexpanded or unexpanded,can expand with increasing temperature. The degree of expansion dependson temperature, polymeric shell polymer composition, encapsulated liquidboiling point, and whether or not the polymeric microspheres arepreexpanded or unexpanded. Thermomechanical analysis (TMA) provides anexcellent tool for measuring expansion of various fluid-filled polymericmicrospheres. The TMA method was carried out on the Thermal MechanicalAnalyzer Q400 manufactured by TA Instruments. A ceramic cup with aninside diameter of 7.54 mm was placed on the sample platform of a TMAQ400. An aluminum lid having an outside diameter of 6.6 mm was placedinside the cup on the platform. A 6.1 mm diameter quartz expansion probewas lowered into the cup containing the lid with preload of 0.06 Ndown-force. Initial sample thickness was measured by the instrument andthe resulting thickness was zeroed by the instrument. The sample cup andlid were then removed from the platform and the lid was removed from thecup. A small amount of fluid-filled polymeric microspheres was placed inthe cup and then the lid was inserted into the cup. The cup and lid wereplaced back on the TMA platform and the quartz probe was lowered intothe cup containing the sample and the lid. The thickness was measuredagain and recorded by the instrument. The TMA was then programmed for atemperature ramp from 30° C. to 250° C. with a ramp rate of 3° C./minand preload of 0.06 N.

The onset temperature of expansion (T_(start)), the maximum expansion,and the temperature at the maximum expansion (T_(max)) are summarized inTable 7 for a few selected fluid-filled polymeric microspheres. Allpolymeric microspheres expanded when heated up to above their T_(start)temperature, including the preexpanded grades.

The reaction exotherm released when casting liquid polyurethane caneasily bring the reaction mixture temperature to well above 100° C.before the material solidifies/gels, causing significant expansion ofpolymeric microspheres with proper thermomechanical properties.

TABLE 7 Maximum Polymeric Microspheres T_(start) (° C .) expansionT_(max) (° C .) Expancel 551DE40d42 109   60% 131 Expancel 551DE20d60103   40% 126 Expancel 461DE20d70 104   62% 128 Expancel 920DE40d30 122  14% 155 Expancel 920DE80d30 128   27% 169 Matsumoto F-65DE 106   24%158 Matsumoto FN-80SDE 106   12% 135 Matsumoto FN-100SSDE 109   17% 156Matsumoto F-190DE 155   29% 189 Matsumoto FN-100SSD 137  940% 159Matsumoto F-30D 85 5445% 122 Matsumoto F-36D 100 8300% 138 MatsumotoR-48D 102 5297% 137 Expancel 031DU40 91 5235% 117 Expancel 461DU20 991966% 129 Expancel 930DU120 122 4989% 174 1/8 wt ratio of 91   96% 128Expancel 031DU40/Expancel 461DE20d70 1/4 wt ratio of 90  145% 116Expancel 031DU40/Expancel 461DE20d70 1/2 wt ratio of 90  282% 116Expancel 031DU40/Expancel 461DE20d70 1/1 wt ratio of 90  308% 120Expancel 031DU40/Expancel 461DE20d70

The temperature of liquid polymer precursor at gel point, T_(gel), needsto be higher than T_(start) for expansion of fluid-filled polymericmicrospheres to occur. Table 8 lists percent expansion at differenttemperatures of various polymeric microspheres. There are differentapproaches to control the T_(gel), such as changing processingtemperature or varying reaction exotherm by using a different % NCOprepolymer. Compared to 8.9% NCO for Adiprene LF750D and 9.1% NCO forAdiprene L325, Adiprene LFG963A has a lower % NCO at 5.7%. When AdipreneLFG963A was cured with MbOCA under the same conditions, the T_(gel) was105° C., much lower than the T_(max) of Expancel 031DU40, but higherthan its T_(start) of 91° C. As a result, uniform pore structures wereobtained without large bubbles over 100 μm present. At 105° C., Expancel031DU40 can expand 24 times of its original volume, as shown in Table 8.

TABLE 8 Polymeric % Expansion at temperature (° C.) Microspheres 100 105110 115 120 Matsumoto 0% 0% 0% 0%    0% F-190DE Matsumoto 0% 0% 0% 0%   0% FN-100SSD Expancel 0% 0% 0% 0%    0% 920DE40d30 Expancel 0% 0% 0%1%    1% 920DE80d30 Matsumoto 0% 0% 0% 1%    2% F-65DE Matsumoto 0% 0%0% 2%    4% FN-80SDE Matsumoto 0% 0% 1% 2%    3% FN-100SSDE Expancel 0%1% 3% 8%   16% 551DE40d42 Expancel 1% 3% 7% 14%    27% 551DE20d60Expancel 0% 1% 9% 22%    38% 461DE20d70 Expancel 0% 0% 0% 0%   57%930DU120 Matsumoto 2670%    3450%    4230%    4990%    5360% F-30DMatsumoto 200%   1700%    3820%    4490%    5010% F-36D Matsumoto 0%1060%    2500%    2900%    3230% F-48D 1/8 wt ratio of 31%  36%  46% 75%    84% Expancel 031DU40/ Expancel 461DE20d70 1/4 wt ratio of 67% 78%  97%  140%    136% Expancel 031DU40/ Expancel 461DE20d70 1/2 wtratio of 113%   127%   154%   276%    239% Expancel 031DU40/ Expancel461DE20d70 1/1 wt ratio of 155%   178%   205%   274%    307% Expancel031DU40/ Expancel 461DE20d70 Expancel 108%   393%   901%   1323%   1666% 461DU20 Expancel 2130%    2421%    2771%    4359%    4693% 031DU40

When T_(gel) of the liquid polymer precursor was higher than T_(max) offluid-filled polymeric microspheres, gas entrapped inside the polymericmicrospheres diffused out of the shell of polymeric microspheres intopolyurethane matrix, causing non-uniform and large pore size in thepolishing pad, negatively affecting polishing performance.

The invention provides polishing pads with excellent conditionerstability. This conditioner stability can improve pad life. In addition,the blend of preexpanded and unexpanded polymeric microspheres allowsfor casting of low density polishing pads not possible by conventionalcasting techniques. Finally, using a blend of preexpanded and unexpandedpolymeric microspheres can create an ideal combination of viscosity forcastability and exothermic heat to achieve effective pore diameters forenhanced polishing.

1. A method of manufacturing a polishing pad suitable for planarizing atleast one of semiconductor, optical and magnetic substrates, the methodcomprising the following: obtaining a liquid polyurethane materialformed from an isocyanate-terminated molecule and a curative agent, theliquid polyurethane material having a T_(gel) temperature and containing4.2 to 7.5 weight percent fluid-filled polymeric microspheres in theisocyanate-terminated molecule, the fluid-filled polymeric microspheresare a blend of preexpanded and unexpanded fluid-filled polymericmicrospheres, the preexpanded and unexpanded fluid-filled polymericmicrospheres each having a T_(start) temperature where diameter of thepreexpanded and unexpanded fluid-filled polymeric microspheres increasesat temperatures equal to or above the T_(start) temperature, with theT_(start) temperature of the unexpanded fluid-filled polymericmicrospheres being less than the T_(gel) temperature of the liquidpolyurethane material; casting the liquid polyurethane materialcontaining the blend of preexpanded and unexpanded fluid-filledpolymeric microspheres, the liquid polyurethane material containing theblend of preexpanded and unexpanded fluid-filled polymeric microsphereshaving a relative viscosity $\frac{\mu}{\mu_{0}}$ of 1.1 to 7, wherein$\frac{\mu}{\mu_{0}} = {1 + {2.5\varphi} + {10.05\varphi^{2}} + {0.00273^{16.6\varphi}}}$where μ is the viscosity of the filled system, μ₀ the viscosity of theunfilled material, $\frac{\mu}{\mu_{0}}$ the relative viscosity, and Φthe volume fraction of the filler; heating and curing the liquidpolyurethane material and the blend of prexpanded and unexpandedfluid-filled polymeric microspheres to a temperature of at leastT_(start) of the unexpanded fluid-filled polymeric microspheres toincrease the diameter of the unexpanded fluid-filled polymericmicrospheres and to form a blend of preexpanded and expandedfluid-filled polymeric microspheres in the liquid polyurethane materialand then solidify the liquid polyurethane material into a polyurethanematrix containing the preexpanded and expanded fluid-filled polymericmicrospheres; and forming the polishing pad from the polyurethane matrixcontaining the preexpanded and expanded fluid-filled polymericmicrospheres.
 2. The method of claim 1 including the additional step ofmixing the blend of preexpanded and unexpanded fluid-filled polymericmicrospheres in the liquid polyurethane material before casting.
 3. Themethod of claim 1 wherein the T_(start) temperature of the unexpandedfluid-filled polymeric microspheres is at least 5° C. less than theT_(gel) temperature of the liquid polyurethane material.
 4. The methodof claim 1 wherein the casting is into a cake mold to form apolyurethane cake structure; and including the additional steps ofremoving the polyurethane cake structure from the mold and skiving thecake structure into multiple polyurethane sheets; and the forming thepolishing pads is from the polyurethane sheets.
 5. The method of claim 1wherein the casting includes pouring the liquid polyurethane materialand the blend of preexpanded and expanded fluid-filled polymericmicrospheres around a transparent block and the forming the polishingpad includes a transparent window in the polishing pad.
 6. A method ofmanufacturing a polishing pad suitable for planarizing at least one ofsemiconductor, optical and magnetic substrates, the method comprisingthe following: obtaining a liquid polyurethane material formed from anisocyanate-terminated molecule and a curative agent, the liquidpolyurethane material having a T_(gel) temperature and containing 4.2 to7.5 weight percent fluid-filled polymeric microspheres in theisocyanate-terminated molecule, the fluid-filled polymeric microspheresare a blend of preexpanded and unexpanded fluid-filled polymericmicrospheres filled with isobutane, isopentane or a mixture of isobutaneand isopentane, the preexpanded and unexpanded fluid-filled polymericmicrospheres each having a T_(start) temperature where diameter of thepreexpanded and unexpanded fluid-filled polymeric microspheres increasesat temperatures equal to or above the T_(start) temperature, with theT_(start) temperature of the unexpanded fluid-filled polymericmicrospheres being less than the T_(gel) temperature of the liquidpolyurethane material; casting the liquid polyurethane materialcontaining the blend of preexpanded and unexpanded fluid-filledpolymeric microspheres, the liquid polyurethane material containing theblend of preexpanded and unexpanded fluid-filled polymeric microsphereshaving a relative viscosity $\frac{\mu}{\mu_{0}}$ of 1.1 to 7, wherein$\frac{\mu}{\mu_{0}} = {1 + {2.5\varphi} + {10.05\varphi^{2}} + {0.00273^{16.6\varphi}}}$where μ is the viscosity of the filled system, μ₀ the viscosity of theunfilled material, $\frac{\mu}{\mu_{0}}$ the relative viscosity, and Φthe volume fraction of the filler; heating and curing the liquidpolyurethane material and the blend of prexpanded and unexpandedfluid-filled polymeric microspheres to a temperature of at leastT_(start) of the unexpanded fluid-filled polymeric microspheres toincrease the diameter of the unexpanded fluid-filled polymericmicrospheres and to form a blend of preexpanded and expandedfluid-filled polymeric microspheres in the liquid polyurethane materialand then solidify the liquid polyurethane material into a polyurethanematrix containing the preexpanded and expanded fluid-filled polymericmicrospheres; and forming the polishing pad from the polyurethane matrixcontaining the preexpanded and expanded fluid-filled polymericmicrospheres.
 7. The method of claim 6 including the additional step ofmixing the blend of preexpanded and unexpanded fluid-filled polymericmicrospheres in the liquid polyurethane material before casting.
 8. Themethod of claim 6 wherein with the T_(start) temperature of theunexpanded fluid-filled polymeric microspheres is at least 5° C. lessthan the T_(gel) temperature of the liquid polyurethane material.
 9. Themethod of claim 6 wherein the casting is into a cake mold to form apolyurethane cake structure; and including the additional steps ofremoving the polyurethane cake structure from the mold and skiving thecake structure into multiple polyurethane sheets; and the forming thepolishing pads is from the polyurethane sheets.
 10. The method of claim6 wherein the casting includes pouring the liquid polyurethane materialand the blend of preexpanded and expanded fluid-filled polymericmicrospheres around a transparent block and the forming the polishingpad includes a transparent window in the polishing pad.